NMR based structure reveals groove binding of mitoxantrone to two sites of [d-(TTAGGGT)](4) having human telomeric DNA sequence leading to thermal stabilization of G-quadruplex

摘要

Interaction of mitoxantrone (MTX) with G-quadruplex, leading to inhibition of telomerase enzyme and anticancer action, is not understood. Titrations of MTX with [d-(TTAGGGT)](4), comprising human telomere single repeat sequence, have been monitored by fluorescence and H-1/P-31 NMR spectroscopy. Binding induces chemical shift changes in GNH (similar to 0.3 ppm), T2/T7/A3 base protons and sequence specific shifts in P-31 resonances. Absence of large downfield shifts in P-31 signals and presence of all sequential NOEs show that classical intercalation of drug between base quartets does not occur. The upfield shift (similar to 0.53 ppm) in 2/3H, 1/4OH and minor shift in 6/7H aromatic protons of MTX in complex rule out end stacking as a possible mode of interaction. The 26 short inter molecular contacts of 1/4OH, 11NH, 6/7H and 12CH(2) protons of MTX with T1, T2, G6, G7 protons in the structure of complex obtained by restrained Molecular Dynamics simulations show binding at grooves accompanied by 4 hydrogen bonds and partial stacking of MTX with base pairs. Interaction causes thermal stabilization, Delta T-m = 35 degrees C, which may be attributed to telomerase inhibition. The present study is the first report on solution structure of mitoxantrone-[d-(TTAGGGT)](4) complex and is significant for structure based designing of anthraquinone derivatives as future drugs. (C) 2018 Elsevier B.V. All rights reserved.